1. Field of the Invention
The invention relates to a block piece for the holding of an optical lens being machined with a coupling part, having an axis of rotation, for the holding and orienting in a workpiece chuck, and a holding part for the securing of the lens, wherein the holding part has a convex or concave holding surface corresponding to a first side of the lens. A holding surface is thus considered to be convex or concave if it is raised relative to the ground, i.e., bulging outward, or sunken, arching inward, regardless of whether it is configured as spherical or aspherical.
2. Description of Related Art
A method for cutting of a contact lens out of a cylindrical blank is already familiar from European Patent EP 1 112 143 B1 and corresponding U.S. Pat. Nos. 6,786,802 and 6,315,650. Here, in order to machine one base side of the blank it is fastened to a first block piece of machinable plastic material and then the machined base side is placed on a second block piece in order to fabricate the front side. The front side of the blank can be aspherical or toroidal in configuration, while the base side toward the blank is spherical in configuration.
When manufacturing aspherical spectacles glasses made from plastic, it is generally customary to bind them to the block piece by a low-melting alloy. For this, a space bounded by the block piece and the lens is filled with the alloy, so that the alloy takes on the form of the aspherical surface of the lens and binds the lens to the block piece. Using the alloy is cost-intensive and detrimental in terms of the time course of the process, since a relatively large amount of alloy is needed. The alloy has to be hot-molded, cooled down, and re-melted for purposes of removal from the block. During the cool-down process, the relative position between the block piece and the lens has to be fixed. The side of the lens being bonded in this case is spherical, in order to guarantee tightness when placed against the block piece for filling with liquid alloy. For aspherical surfaces, a sealing lip is provided between the block piece and the lens, ensuring a tight abutment.
Alternatively, Japanese Patent Application JP 11198014 A describes how to hold the lens by means of a deformable wax or how to mold this against the lens and thereby fix the lens.